The lines Romeo speaks are
"Thou detestable maw, thou womb of death,
Gorg'd with the dearest morsel of the earth,
Thus I enforce thy rotten jaws to open,"
Translates to -
You hateful belly, you womb of death,
Stuffed full with the dearest morsel of the earth,
I will force your rotten jaws to open,
The examples of personification, giving human qualities to things that are not human, are calling the tomb a belly, womb, saying it has eaten its fill of Juliet, and calling the tomb's doors rotten jaws.